Means for raising liquids from great depths



June 26, 1956 E. w. SMITH 2,751,848

MEANS FOR RAISING LIQUIDS FROM GREAT DEPTHS Filed July 11, 1951 A; L I'h A 1'1 Z 4w 16 INVENTOR.

United States Patent MEANS FOR RAISING LIQUIDS FROM GREAT DEPTHS EdwardW. Smith, Melrose Highlands, Mass. Application July 11, 1951, Serial No.236,152

1 Claim. (Cl. 103-75) The present invention relates to a means ofimproving the efiiciency of removal of liquids from great depths as inpumping oil or water wells and the like.

While attempts have been made to use wave motion in a liquid column forthis purpose, it appears that the principles have not been correctlyapplied to obtain the desired results.

In order to accomplish the desired result, it is necessary to use thenatural resonance of the liquid column in which case the pressure nodeor nodes of the standing wave in the column are in the column of theliquid away from the end which must have velocity maXima in oppositedirectional phase. A further criterion in the easy operation of such asystem is that in the initial transient state of operation, until thesteady state resonance con-- dition has been reached, the amplitude ofmotion applied at the outlet end or top end of the system must be slowlyincreased. In fact full amplitude should not be applied immediatelysince the forces and power required may be many times the naturaloperating forces and power.

By directional phase is meant that as the liquid in the column movesdownward at the-top, it must move upward at the bottom and vice versa.This means that the valve at the lower end of the column opens to admitliquid as the piston at the top end of the column is compressing theliquid so thatafter the liquid is drawn into the column at the base, itthen flows off at the top during the next succeeding half cycle.

In the specification below, Figure 1 shows somewhat diagrammatically theinvention which may be carried out in various construction forms by theuse of well known standard elements which will be hereinafter mentionedand Figure 2 shows a detail of an element of Figure 1.

The sense in which the expression efficiency is used in the presentinstance can best be understood from the following. Suppose, forexample, that a liquid such as water is to be pumped from a pool at thebottom of a well 1000 feet as shown in the drawing 1 where 1representsthe pool and 2 the well casing. I

Suppose now that the water is brought to the'surface under atmosphericpressure by filling and raising a container to the surface by a cable orthe like. The amount of energy required per gallon of Water so liftedwill be the weight of the Water times the distancethrough which it israised. Thus if the water being pumped weighs 62.5 pounds per cubicfoot, one gallon would weigh 8.35 pounds and the energy required toraise one gallon to the surface would be 8350 foot pounds, neglecting ofcourse the weight of the container and cable.

Normally of course, such a procedure would not be followed as in generala pump would be placed at the bottom of the well to force the water tothe surface. Under such conditions an entirely difierent situationprevails because the pump must not only provide the energy to liftonegallon to the surface, but in addition must do soagainst a 1000 foothead of water. In such a case the pressure per square inch at the bottomof the column would be approximately 434 pounds per square inch ice andzero at the top. Therefore it will be apparent that the pump, in raisinga unit volume of water to. the surface must not only supply the energyrequired to physically raise the water from the depth, but must inaddition do so against an average pressure of 217 lbs/sq. inch.

If we assume, for simplicity sake that the. casing has an internal crosssection of one square inch, the work required to raise one gallon ofwater through it will be 217,000 foot pounds to overcome the head ofwater plus 8350 foot pounds to raise the gallon of water. It will beclear therefore, that of the total of 225,350 foot pounds of energyrequired to raise a gallon of water up from the bottom of a 1000 footwell under the above conditions, over 96% is wasted in simply overcomingthe pressure head.

The means whereby this situation is alleviated in the present inventioncan best be understood from the following.

If one end of a closed pope, as for instance the well casing 2, full ofliquid 3 is fitted with a close fitting reciprocating piston or fluiddisplacement member 4, a Wave of alternating pressure and ran'faction isproduced, which travels along the liquid in the pipe at a velocity whichis determined by the constants of the liquid, in the case of waterapproximately 1500 meters per second. If the frequency of reciprocationis adjusted to the point where it corresponds to a one-half wavelengthin the liquid in the column, the column will expand and contract inlength in unison with the motion of the piston.

Let us now consider the case of such a pipe set vertically in the groundas in the case of a deep water or oil well as shown in the drawing andthat the bottom of the pipe is fitted with a ball check valve 5 openinginwardly.

Normally of course, the column of liquid in the pipe will exert apressure on the valve tending to keep it closed. If now the piston isset into reciprocation a similar standing wave is established in thecolumn of liquid and if the speed of reciprocation is chosen as aboveindicated.

the column will tend to elongate and contract in unison with the piston.During the portion of the cycle when the piston is in its most downwardposition, assuming that steady state conditions have been established,the bottom of the column will be iniits most upward position and oil orWater, as the case may be, can flow into the bottom of the columnfilling in the space created .by the contraction of the colunm. q i

As the oscillating column starts to elongate again, pressure will beexerted on the liquid just drawn in and simultaneously the piston willbe beginning the upward portion of its travel as will also the top ofthe column of liquid. Normally of course, the complete expansion of thecolumn when added to the depth of liquid drawn in at the bottom would bemore than the piston travel in the upward direction. It will be notedhowever, that as the piston rises past the normal neutral level of thetop of the column, a port 8 is opened allowing the excess liquid to beforced out, the amount thus forced out being equivalent to what wastaken in at the bottom of the column. When the excess liquid is forcedout the piston starts downward again on a new cycle,

the port 8 isclosed by the piston and the cycle is repeated.

In this way the energy required to lift to the top the liquid drawn inat the bottom at each stroke is substantially only the energy requiredto lift the same weight through the height-of the column.

The validity of this statement can perhaps best be appreciated from aconsideration of the fact that when the column expands from the baseprovided by the liquid energy resident in the contracted column wil1.beused to raise the Whole column one foot. It is clear that from an energystandpoint there is no difierence between raising a one foot deep layerof liquid through 1000 feet than there is in raising a 1000 foot columnby one foot. The energy input from the piston at each stroke is thereforthat required'to raise to the surface at each stroke the amount ofliquid drawn in at the bottom during the same period. a

In considering the detailed application of the present invention to aspecific instance the following may be helpful. Suppose that we have asituation such as is depicted in the figure where it is desired to pumpwater from a pool at the bottom; ofa well 1000 feet deep. It will beunderstood that the same procedure would be followed for pumping otherliquids, such as oil, except that the wheref, A, and c are respectivelythe frequency, wavelength and velocity of transmission.

In this particular instance, 1000 feet is to be taken as /2 andfurthermore the velocity of sound in water may be taken as 4920 feet/second.

Therefor,

f =%%=2.46 cycles/sec.

The necessary frequency of operation having now been determined it willnext be appropriate to determine the elastic modulus of the water as apreliminary to determining the amplitude of motion of one end of thecolumn for a given maximum operating pressure. This factor may bearrived at from the velocity of pulse transmission,

in water and its density which are connected by the relationship where Eis the elastic modulus and, p is the density. 1

Converting into metric units, We have 4920 feet/sec=..l50,000, cm/sec.

62.5 lbs/cu. ft.,=1 gram/cc E.=225()8 dynes/cm. =327,000 lbs/sq. in.

and

The maximum operating pressure in the column which tends to elongate andcontract it, is toa certain extent a matter of choice although it isdesirable to keep it reasonably low consistent with the desired pumpingrate because of cavitation problems should the water containdissolvedgas.

We can now. proceed either by determining the operating pressure for agiven piston stroke or vice versa.'

Suppose we decide on a piston strolgeof 4 inches remembering that in. ahalf wave oscillating column the total compression of-the column willbetwice the compression" at either end. The operating pressure per squareinch will then be dAE l where at is the compression, l is the length ofthe column, and A its cross sectional area.

Substituting we have In considering this figure it should be rememberedthat it is the maximum internal pressure exerted in the oscillatingcolumn tending to increase and decrease its length and is not thepressure which must be exerted by the piston which is many times lessthan this amount. If the column were simply contracting and elongatingas a half wave oscillator no energy would need be put in by the pistonafter the column was once set in oscillation if it were not for theviscous losses in the liquid, friction losses on the pipe walls, etc.plus the energy required to raise the water being pumped. Neglectingsuch losses for the moment, the, amount of work required toraise 1gallon of water from this depth, as we have already seen is 8350 footpounds. Since the piston frequency will be 2.46 cycles per second asalready determined this means 8350 (2.46)=20,550 ft. lbs/sec.

=3.74 horsepower In other words, 3.74 H. P. to pump 147.5 gals/min.Mention has already been made of the fact that the maximum pressureexerted on the column of water by the piston is many times less than,the pressure internal in the column which tends to elongate andcontract it during operation.

. As. an example, suppose we wish to design the pump required to give acapacity of 50 gallons per minute using" the operating pressures justcomputed.

50 gallons/min=78.2 cu. in./stroke Using our assumed amplitude of 4inches, the area of the piston would then be 19.55 square inchesand'the' piston diameter, 5 inches.

The power required would be =6950 ft. lbs/sec.

:944 Watts/50 gals/min Since the piston is describing sinusoidal motionthe powerwhich it is delivering may be expressed as where F, a and w arerespectively the maximum force in Neglecting viscous and frictionlosses, the maximum pressure: which must be exerted'by the piston tokeep the;

column in oscillation as a /2 wavelength oscillating col umn is onlyabout 6.3% of what would be requiredLto compressor elongate the columnunder static conditions.

To summarize then, the method of operation wouldbe to operate the pistonat a speed corresponding to the half wave frequency of the liquid column(or an odd harmonic of it). In so doing a standing wave is establishedin the liquid column which has the efiect of shortening and elongatingthe column from both ends toward or away from the middle, i. e. thepiston amplitude is reproduced at the bottom of the column. In so doingit removes the pressure periodically which would normally act to openthe check valve at the bottom and allow liquid to flow into the limit ofthe displacement. On the re verse half of the cycle the column willdescend against the liquid so drawn in thus closing the check valve.

Normally of course this would mean that the whole column would rise by asimilar amount. In the present instance, however, the valve or port atthe top of the column allows the liquid to escape. Under theseconditions the pump simply supplies the energy required to lift theliquid to the top which is drawn in at the bottom on each stroke, plusfriction losses of course, and the necessity of pumping against a 1000foot head is avoided. In putting such a system in operation certainspecial precautions must be taken because of the resonant nature of theoperation. Attention has already been called to the fact that thepressures required on the piston surface may be only 6% or thereabouts,of the actual internal pressures in the column. In other Words, thepiston pressure which would be needed to start the column in oscillationat the amplitude discussed above, from rest, could well be many timesthat required for normal operation once the column was oscillating atresonance.

In fact, unless special precautions are taken, it would be nearlyimpossible to start the column in oscillation at all by means of apiston directly connected to an eccentric giving the desired amplitudeunless the motor driving the eccentric were enormously larger than wouldbe needed under running conditions. For this reason it is practicallyessential to provide some means whereby the stroke of the piston can bereduced until resonant conditions have been established. This may beaccomplished by introducing in the crank arm 6 connecting the piston tothe eccentric an hydraulic arrangement 7, such as is shown in my PatentNo. 2,541,112 which will permit the piston to operate at reducedamplitude until such resonance conditions have been established. Figure2 shows somewhat diagrammatically the element 7 which comprises acylinder 9 having a partitioning piston wall 15 reciprocatcd by a shaft10 which may extend through both ends of the cylinder 9. Smallconnecting passages 16 through the piston permit the building up of theamplitude of motion of the piston to a resonant point after the systemhas once been started in operation when connected as shown in Figure 2of my Patent No. 2,541,112 referred to above.

I am cognizant of the fact that various attempts have been made in thepast to utilize somewhat the general principles described herein, but,so far as I am aware, they have not been successful. This hasundoubtedly been due in the main to the lack of two major improvementsdisclosed herein; one, the operation of the column at its natural periodof oscillation to avoid the pressures which would otherwise be presentat the bottom of the column, and secondly, the provision of meanswhereby the piston amplitude may be automatically reduced initially topermit the column to be supplied with energy at its resonant frequencyuntil steady state conditions of oscillation have been established.

While resonance of the liquid column may be established for the wholecolumn from the top of the shaft to the check valve at the bottom, it isintended that the reference to top and bottom is to include a section ofthe column used to establish the half or multiple half wave lengthresonance.

Having now described my invention, I claim:

In combination with a well casing having a wall providing an enclosedconfined liquid well column, means for drawing the liquid from the topof the well casing comprising a one way valve at the bottom of the wellcasing permitting liquid to flow in the well casing, an outlet in thewell casing above the top of the liquid well column, a fluiddisplacement member at the top of the liquid well column, meansconnected to said member for periodically applying motion to the memberat the resonant frequency of the liquid well column wherein the liquidwell column is one half wave length and odd number of half wave lengthsreferred to the frequency and means for gradually increasing themagnitude of the applied aforesaid motion to said fluid displacementmember until full resonance in the liquid well column of the well hasbeen built up to the desired value, said last mentioned means comprisinghydraulic coupling means having two opposing sections connected betweenthe displacement member and the means for periodically applying motionto said member and further having pressure release means between theopposing sections of said coupling means.

References Cited in the file of this patent UNITED STATES PATENTS1,730,336 Bellocq Oct. 1, 1929 2,232,678 Dickinson Feb. 25, 19412,541,112 Smith Feb. 13, 1951 FOREIGN PATENTS 324,598 Great Britain Jan.30, 1930

